catalyst substance that speeds up a chemical reaction but - CHEM - 1010 View Full Document -catalyst: substance that speeds up a chemical reaction but itself remains unchanged after the reaction is over -example: oxidation of SO2 to SO3 in atmosphere; SO3 contributes to “acid rain” -reaction occurs in atmosphere because of the presence of another atmospheric pollutant which acts as a catalyst; sunlight is energy source -reaction intermediate: not present at the beginning, but is both created and destroyed during reaction -if not a catalyst, then it’s a reactant -all catalysts function by providing an alternate reaction pathway that has a lower activation energy than the uncatalyzed -the heat of reaction remains unchanged in presence of catalyst, however, the rates of both the forward and reverse reactions are increased -doesn’t alter results, only reaction speed 8.4 Biochemical Catalysts -biological catalysts are almost always protein molecules called catalysts -extremely selective; only one specific set of reactants will bind to a specific enzyme molecule -”lock and key” fit; enzyme binds its substrates to form enzyme-substrate complex that turns into enzyme-product complex - -substrate and -product are connected by transition state or activated complex

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Sign up to access the rest of the document. TERM Catalysts Catalysts Introduction Have you ever heard anyone say that an event was 'a catalyst for change'? A teacher might say it of a test, if a student suddenly improved their performance after receiving poor marks. In a sense, the test result was the catalyst that sparked off a reaction in the student, stirring them into action! In this unit we will be looking at chemical catalysts that affect the rates of chemical reactions. Catalysis We can speed up some reactions by adding a substance known as a catalyst A catalyst is a substance that alters (usually speeds up) the rate of a chemical reaction, but remains chemically unchanged itself at the end of the reaction.catalyst. Look at the reaction in Fig.1 below. It shows the breakdown of hydrogen peroxide solution: hydrogen peroxide Figure 1. An example of catalysis The reaction in Fig.1 takes place rapidly when manganese(IV) oxide is present in the mixture. However, the manganese(IV) oxide is unchanged when the reaction has finished: it acts as a catalyst. How would you perform a test to identify the gas given off in the experiment in Fig.1?

Bubble it through limewater, which would turn cloudy Apply a lighted splint to ignite the gas, which would burn with a 'squeaky' pop Insert a glowing splint into the gas, and the splint would re-light At the end of this reaction, when all the hydrogen peroxide has broken down, the catalyst remains chemically unchanged. We could filter off the manganese(IV) oxide and use it again. So we can define a catalyst in the following way: A catalyst is a substance that speeds up a chemical reaction but remains chemically unchanged at the end of the reaction . A catalyst does not appear in the chemical equation for the reaction that it catalyses. It is the same substance before and after the reaction. We can show its presence by including it above the arrow in the equation: Manganese(IV) oxide is also a catalyst for the breakdown of potassium chlorate(V). The potassium chlorate(V) forms potassium chloride and oxygen when heated. Which is the correct word equation A word equation is a way of describing what we start with and what is formed in a chemical equation, e.g. magnesium + oxygen magnesium oxide. word equation for the catalysed reaction?

There are also some substances that act as 'negative catalysts', slowing down chemical reactions. We call these inhibitors. Explaining how catalysts work In order for colliding particles to react together, they must have enough energy to exceed the activation energy needed for the reaction. We can show this on an energy level (or energy profile) diagram, as in Fig.2: Energy level diagram (for an exothermic reaction). But look what happens when we add a catalyst: The effect of a catalyst on activation energy. The catalyst provides a different route for the reaction  a route with a lower activation energy The activation energy is the minimum amount of energy required for reactants to form products in a chemical reaction.activation energy. This means that more of the particles in the reaction mixture have sufficient energy to react. It's a bit like lowering the bar in a high-jump competition: a lot more people can get over the bar at the lower height. Which statement about catalysts is correct? Catalysts work by increasing the energy of reactant particles. Catalysts work by increasing the activation energy of a reaction. Catalysts work by lowering the activation energy of a reaction.

Examples of catalysis in industry Catalysts are very important in many chemical processes in industry. They speed up reactions, making processes more efficient. So lots of research goes into finding the best catalyst for particular reactions. Look at the table below which shows the catalysts used in some industrial processes: Substance manufactured Ziegler catalyst (titanium(IV) chloride and triethyl aluminium) Which of the catalysts in the table above are transition metals or compounds of a transition metal? Iron BBC - Standard Grade Bitesize Biology - Enzymes and aerobic respiration : Revision, Page 2 Next What are Enzymes? A catalyst is a substance which speeds up a chemical reaction but is left unchanged after the reaction. Enzymes [enzymes: proteins which catalyse or speed up chemical reactions inside our bodies] are biological catalysts present in all living cells. Without enzymes the reactions in living cells would be far too slow to keep life going. Enzymes are all made of protein and are specific. This means that one enzyme will work on one substrate [substrate: a substance on which enzymes act] (starting substance).

The general word equation for an enzyme reaction is - Substrate enzymes Product In this video, you can see a demonstration of how the enzyme catalase (which is present in the liver in large amounts) breaks down hydrogen peroxide to make it harmless. Video: Enzymes In order to see this content you need to have both Javascript enabled and Flash installed. Click this audio clip to find out more about how enzymes work. In order to see this content you need to have both Javascript enabled and Flash installed. Page Chemical Equilibrium A given chemical reaction system is defined by a balanced net chemical equation which is conventionally written as reactants → products The first thing we need to know about a chemical reaction represented by a balanced equation is whether it can actually take place. If the reactants and products are all substances capable of an independent existence, then in principle, the answer is always "yes". This answer must be qualified, however, by the following considerations: How complete is the reaction? That is, what fraction of the reactants are converted into products? Some reactions convert essentially 100% of reactants to products, while for others the quantity of products may be undetectable.

Many are somewhere in between, meaning that significant quantities of all components remain at the end. Later on, in another part of the course, you will learn that the tendency of a reaction to occur can be predicted entirely from the properties of the reactants and products through the laws of thermodynamics. How fast does the reaction occur? Some reactions are over in microseconds; others take years. The speed of any one reaction can vary over a huge range depending on the temperature, the state of matter (gas, liquid, solid) and the presence of a catalyst. Unlike the question of completeness, there is no simple way of predicting reaction speed. What is the mechanism of the reaction? What happens, at the atomic or molecular level, when reactants are transformed into products? What intermediate species (those that are produced but later consumed so that they do not appear in the net reaction equation) are involved? This is the microscopic, or kinetic view of chemical change, and cannot be predicted by theory as it is presently developed and must be inferred from the results of experiments. A reaction that is thermodynamically possible but for which no reasonably rapid mechanism is available is said to be kinetically limited .

Conversely, one that occurs rapidly but only to a small extent is thermodynamically limited . As you will see later, there are often ways of getting around both kinds of limitations, and their discovery and practical applications constitute an important area of industrial chemistry. 2 What do we mean by "equilibrium"? Basically, the term refers to what we might call a "balance of forces". In the case of mechanical equilibrium, this is its literal definition. A book sitting on a table top remains at rest because the downward force exerted by the earth's gravity acting on the book's mass (this is what is meant by the "weight" of the book) is exactly balanced by the repulsive force between atoms that prevents two objects from simultaneously occupying the same space, acting in this case between the surfaces of the table and the book. If you pick up the book and raise it above the table top, the additional upward force exerted by your arm destroys the state of equilibrium as the book moves upward. If you wish to hold the book at rest above the table, you adjust the upward force to exactly balance the weight of the book, thus restoring equilibrium.

An object is in a state of mechanical equilibrium when it is either static (motionless) or in a state of unchanging motion. From the relation f = ma, it is apparent that if the net force on the object is zero, its acceleration must also be zero, so if we can see that an object is not undergoing a change in its motion, we know that it is in mechanical equilibrium. Thermal equilibrium Another kind of equilibrium we all experience is thermal equilibrium. When two objects are brought into contact, heat will flow from the warmer object to the cooler one until their temperatures become identical. Thermal equilibrium arises from the tendency of thermal energy to become as dispersed or "diluted" as possible. A metallic object at room temperature will feel cool to your hand when you first pick it up because the thermal sensors in your skin detect a flow of heat from your hand into the metal, but as the metal approaches the temperature of your hand, this sensation diminishes. The time it takes to achieve thermal equilibrium depends on how readily heat is conducted within and between the objects; thus a wooden object will feel warmer than a metallic object even if both are at room temperature because wood is a relatively poor thermal conductor and will therefore remove heat from your hand more slowly.

Thermal equilibrium is something we often want to avoid, or at least postpone; this is why we insulate buildings, perspire in the summer and wear heavier clothing in the winter. Chemical equilibrium When a chemical reaction takes place in a container which prevents the entry or escape of any of the substances involved in the reaction, the quantities of these components change as some are consumed and others are formed. Eventually this change will come to an end, after which the composition will remain unchanged as long as the system remains undisturbed. The system is then said to be in its equilibrium state, or more simply, "at equilibrium". Equilibrium and closed systems Reactions that take place in open systems will not be reversible if products can escape. It is important to bear in mind that equilibrium can only be achieved if none of the reactants or products is allowed to escape from the system; such a system is said to be closed. As a simple example, consider the vaporization of water: H2O(l) → H2O(g) If some water is placed in a closed container, the partial pressure of water vapor in the space above the liquid will gradually build up to a constant (equilibrium) value which depends mainly on the temperature.

But if the water is left to vaporize in the open, the water vapor will simply be dispersed into the environment, the system is open and the equilibrium state will never be reached. Why reactions go toward equilibrium What is the nature of the "balance of forces" that drives a reaction toward chemical equilibrium? It is essentially the balance struck between the tendency of energy to reside within the chemical bonds of stable molecules, and its tendency to become dispersed and diluted. Exothermic reactions are particularly effective in this, because the heat released gets dispersed in the infinitely wider world of the surroundings. In the reaction represented here, this balance point occurs when about 60% of the reactants have been converted to products. Once this equilibrium state has been reached, no further net change will occur. (The only spontaneous changes that are allowed follow the arrows pointing toward maximum dispersal of energy.) A more complete explanation of this must be deferred until the discussion of thermodynamics in a later chapter . Chemical equilibrium is something you definitely want to avoid for yourself as long as possible. The myriad chemical reactions in living organisms are constantly moving toward equilibrium, but are prevented from getting there by input of reactants and removal of products.

So rather than being in equilibrium, we try to maintain a "steady-state" condition which physiologists call homeostasis — maintenance of a constant internal environment. For more on this, see this Wikipedia article . Equilibrium is death! For the time being, it's very important that you know this definition: A chemical reaction is in equilibrium when there is no tendency for the quantities of reactants and products to change. The direction in which we write a chemical reaction (and thus which components are considered reactants and which are products) is arbitrary. Thus the two equations H2 + I2 → 2 HI 2 HI → H2 + I2 "dissociation of hydrogen iodide" represent the same chemical reaction system in which the roles of the components are reversed, and both yield the same mixture of components when the change is completed. This last point is central to the concept of chemical equilibrium. It makes no difference whether we start with two moles of HI or one mole each of H2 and I2; once the reaction has run to completion, the quantities of these two components will be the same.

In general, then, we can say that the composition of a chemical reaction system will tend to change in a direction that brings it closer to its equilibrium composition. Once this equilibrium composition has been attained, no further change in the quantities of the components will occur as long as the system remains undisturbed. It's the same both ways The two diagrams below show how the concentrations of the three components of this chemical reaction change with time. Examine the two sets of plots carefully, noting which substances have zero initial concentrations, and are thus "products" of the reaction equations shown. Satisfy yourself that these two sets represent the same chemical reaction system, but with the reactions occurring in opposite directions. Most importantly, note how the final (equilibrium) concentrations of the components are the same in the two cases. Whether we start with an equimolar mixture of H2 and I2 (left) or a pure sample of hydrogen iodide (shown on the right, using twice the initial concentration of HI to keep the number of atoms the same), the composition after equilibrium is attained (shaded regions on the right) will be the same. The equilibrium composition is independent of the direction from which it is approached. 3 What is a reversible reaction?

A chemical equation of the form A → B represents the transformation of A into B, but it does not imply that all of the reactants will be converted into products, or that the reverse reaction B → A cannot also occur. In general, both processes (forward and reverse) can be expected to occur, resulting in an equilibrium mixture containing finite amounts of all of the components of the reaction system. (We use the word components when we do not wish to distinguish between reactants and products.) If the equilibrium state is one in which significant quantities of both reactants and products are present (as in the hydrogen iodide example given above), then the reaction is said to be incomplete or reversible . The latter term is preferable because it avoids confusion with "complete" in its other sense of being completed or finished, implying that the reaction has run its course and is now at equilibrium. If it is desired to emphasize the reversibility of a reaction, the single arrow in the equation is replaced with a pair of hooked lines pointing in opposite directions, as in A B. Note that there is no fundamental difference between the meanings of A → B and A B. Some older textbooks just use A = B.

A reaction is said to be complete or quantitative when the equilibrium composition contains no significant amount of the reactants. A reaction that is complete when written in one direction is said "not to occur" when written in the reverse direction. In principle, all "elementary" (simple one-step) chemical reactions are reversible, but this reversibility may not be observable if the fraction of products in the equilibrium mixture is very small, or if the reverse reaction is very slow (the chemist's term is " kinetically inhibited ") Why some reactions are not reversible Chemical changes that take place in multiple steps, and thus involve many different reactions, tend to be irreversible; "you can't put Humpty Dumpty together again". But even relatively simple reactions can be almost impossible to reverse if the thermodynamic stability of the products is far greater than that of the reactants. Here are some examples of irreversible reactions that we all see in our daily lives: The chemistry of combustion and flames is hugely complicated, with different processes taking place in different parts of the flame. There is no way you can "un-burn" a combustible object! Heating egg-white causes its proteins to unfold into a permanently entangled mess.

(More here .) Corrosion of iron results in the formation of a number of iron oxides that are more stable than iron itself; there is no going back! Browning of toast (and of meats) is the result of the Maillard reaction in which amino acids (from the protein material) combine with certain types of sugars to produce a large variety of brown (and flavorful) complex products. How did Napoleon Bonaparte help discover reversible reactions? We can thank Napoleon for bringing the concept of reaction reversibility to Chemistry. Napoleon recruited the eminent French chemist Claude Louis Berthollet (1748-1822) to accompany him as scientific advisor on the most far-flung of his campaigns, the expedition into Egypt in 1798. Once in Egypt, Berthollet noticed deposits of sodium carbonate around the edges of some the salt lakes found there. He was already familiar with the reaction Na2CO3 + CaCl2 → CaCO3 + 2 NaCl which was known to proceed to completion in the laboratory. He immediately realized that the Na2CO3 must have been formed by the reverse of this process brought about by the very high concentration of salt in the slowly-evaporating waters.

This led Berthollet to question the belief of the time that a reaction could only proceed in a single direction. His famous textbook Essai de statique chimique (1803) presented his speculations on chemical affinity and his discovery that an excess of the product of a reaction could drive it in the reverse direction. Unfortunately, Berthollet got a bit carried away by the idea that a reaction could be influenced by the amounts of substances present, and maintained that the same should be true for the compositions of individual compounds. This brought him into conflict with the recently accepted Law of Definite Proportions (that a compound is made up of fixed numbers of its constituent atoms), so his ideas (the good along with the bad) were promptly discredited and remained largely forgotten for 50 years. (Ironically, it is now known that certain classes of compounds do in fact exhibit variable composition of the kind that Berthollet envisioned.) 4 How reactions approach equilibrium The law of mass action Berthollet's ideas about reversible reactions were finally vindicated by experiments carried out by others, most notably the Norwegian chemists (and brothers-in-law) Cato Guldberg and Peter Waage.

During the period 1864-1879 they showed that an equilibrium can be approached from either direction. Recall the example in Section 2 above, in which the reactionsH2 + I2 → 2HI and 2HI → H2 + I2, when carried out under the same conditions of temperature and pressure, yield the same equilibrium concentrations of the three gases. If we wish to emphasize this fact, we can express this process by the single equation H2 + I2 2HI. More generally, we can consider that any reversible reaction of the form aA + bB → cC + dD is really a competition between a "forward" and a "reverse" reaction. When a reaction is at equilibrium, the rates of these two reactions are identical, so no net . Reaction rates depend on the mechanism of the reaction that is, on what actually happens to the atoms as reactants are transformed into products. Reaction mechanisms cannot generally be predicted, and must be worked out experimentally. Also, the same reaction may have different mechansims under different conditions. As a chemical change proceeds, the quantities of the components on one side of the reaction equation will decrease, and those on the other side will increase.

Eventually the reaction slows down and the composition of the system stops changing. At this point the reaction is in its equilibrium state , and no further change in composition will occur as long as the system is left undisturbed. For many reactions, the equilibrium state is one in which components on both sides of the equation (that is, both reactants and products) are present in significant amounts. Such a reaction is said to be incomplete or reversible . The equilibrium composition is independent of the direction from which it is approached; the labeling of substances as "reactants" or "products" is entirely a matter of convenience. (See the hydrogen iodide reaction plots above.) The law of mass action states that any chemical change is a competition between a forward reaction (left-to-right in the chemical equation) and a reverse reaction. The rate of each of these processes is governed by the concentrations of the substances reacting; as the reaction proceeds, these rates approach each other and at equilibrium they become identical.

From the above, it follows that equilibrium is a dynamic process Definition of catalyst - Chemistry Dictionary Definition of Catalyst A catalyst is a substance that speeds up a chemical reaction, but is not consumed by the reaction; hence a catalyst can be recovered chemically unchanged at the end of the reaction it has been used to speed up, or catalyze. Discussion In order for chemicals to react, the species involved in any reaction must undergo a rearrangement of chemical bonds. The slowest step in the bond rearrangement produces what is termed a transition state - a chemical species that is neither a reactant nor a product, but is an intermediate between the two. Energy is required to form the transition state. This energy is called the Energy of Activation, or Ea. Reactants with energy lower than Ea cannot pass through the transition state to react and become products. A catalyst works by providing a different route, with lower Ea, for the reaction. In any given time interval, the presence of a catalyst allows a greater proportion of the reactant species to acquire sufficient energy to pass through the transition state and become products. Catalysts cannot shift the position of a chemical equilibrium - the forward and backward reactions are both accelerated so that the equilibrium constant Keq is unchanged.

However, by removing products from the reaction mixture as they form, the overall rate of product formation can in practice be increased. Search the Dictionary for More Terms The Effect of pH on the Activity of Catalase :: Papers The Effect of pH on the Activity of Catalase Length: 2256 words (6.4 double-spaced pages) Rating: Excellent The Effect of pH on the Activity of Catalase Planning Experimental Work Catalase is a type of enzyme found in different types of foods such as potatoes, apples and livers. It speeds up the disintegration of hydrogen peroxide into water because of the molecule of hydrogen peroxide (H2O2) but it remains unchanged at the end of the reaction. This is a type of reaction where a molecule is broken down into smaller pieces. It is called an anabolic reaction. This experiment is the breakdown of hydrogen peroxide to form water and oxygen in the air. Catalase is found in a cell organelle called the peroxisome. Peroxisomes in animal cells are occupied in the decomposition of fatty acids, and the separation of cholesterol and bile acids. White blood cells create hydrogen peroxide to destroy bacteria. Hydrogen Peroxide is a result of fatty acid oxidization.

Catalase prevents the hydrogen from damaging the cell itself. Peroxisomes in plant cells are concerned in photorespiration and symbiotic nitrogen fixation (the breaking apart of the nitrogen molecule, N2, to re-activate nitrogen atoms). Hydrogen Peroxide is produced during these chemical processes and must be removed to prevent further damage. Oxygen-requiring bacteria produce Hydrogen Peroxide as a result of metabolism. The previous mentioned fact is used when identifying bacteria. If Hydrogen Peroxide is added to a bacterial settlement and bubbles are created, this is evidence of oxygen production and confirms that the settlement is aerobic. Through research in books I have found out that the optimum pH condition for Catalase is pH 7.52. Enzymes are natural biochemical catalysts. They are produced by the cell to perform very specific functions. Also, they are biological catalyst produced in cells, and capable of speeding up the chemical reactions necessary for life. They are large, complex proteins, and are highly specific, each chemical reaction requiring its own particular enzyme. The enzyme's specificity arises from its active site, an area with a shape corresponding to part of the molecule with which it reacts (the substrate).

How to Cite this Page MLA Citation: The enzyme and the substrate slot together forming an enzyme-substrate complex that allows the reaction to take place, after which the enzyme falls away unaltered. The activity and efficiency of enzymes are influenced by various factors, including temperature and pH conditions. Temperatures above 60º C/140ºF damage (denature) the intricate structure of enzymes, causing reactions to cease. Each enzyme operates best within a specific pH range, and is denatured by excessive acidity or alkalinity. Digestive enzymes include amylases (which digest starch), lipases (which digest fats), and proteases (which digest protein). Other enzymes play a part in the conversion of food energy into ATP; the manufacture of all the molecular components of the body; the replication of DNA when a cell divides; the production of hormones; and the control of movement of substances into and out of cells. Enzymes have many medical and industrial uses, from washing powders to drug production, and as research tools in molecular biology. They can be extracted from bacteria and moulds, and genetic engineering now makes it possible to tailor an enzyme for a specific purpose.

The most abundant enzyme is ribulose biphosphate carboxylase. It is found in chloroplasts and associated with photosynthesis. (Hutchinson Educational Encyclopaedia, 2000) Catalyse is an enzyme present in the cells of all living things and aerobic bacteria. It encourages the change of hydrogen peroxide, a powerful and dangerous oxidizing agent, to water and oxygen present in the air. Collision theory explains how chemical reactions occur and why rates of reaction differ. For a reaction to occur, particles must collide. If the collision causes a chemical change it is referred to as a fruitful collision. (Hutchinson Educational Encyclopaedia, 2000) Enzymes increase the rate of exergonic reactions by decreasing the activation energy of the reaction. Exergonic reactions are those in which the free energy of the concluding state is lower than the free energy of the opening state. These reactions take place unexpectedly. However, the rate of an unexpected reaction may not be very great. This is because an energy hurdle must first be defeated. This hurdle is called the activation energy of the reaction. [IMAGE] By decreasing the activation energy, more substrate is changed to product in a certain amount of time.

That is, the enzyme increases the rate of the reaction. The activity of catalase can be measured by finding the rate of which the oxygen gas is released from the breakdown of Hydrogen Peroxide. The books and resources I used were: Ø OCR Staged Assessment Phase 1 Module by Mary Janes Ø Energy and Chemistry Ø - searched for hydrogen peroxide, enzymes & catalysts. Aim: The aim of my experiment is to see the effect of pH on the activity of catalase. The buffer solutions that I am using are the following: 4.4, 5.2, 6.5, 7.5 and 8.4. I will be varying the volume of pH and I will be measuring the time. I will keep some of the variables constant throughout the investigation such as the amount of potato and the amount of buffer solution. Also, the amount of Hydrogen Peroxide will be kept the same all the way through. I predict that as soon as I pour the pH Buffer Solution and Hydrogen Peroxide onto the potato, I will obtain hydrogen gas, which will form in my measuring cylinder. This will happen because the potato and the solution react fast to give me my products.

I think this because as the pH value decreases the reaction time will increase and the rate of reaction will increase so when it falls from 8.4 to 4.4 the reaction time will increase. This is because the collision theory states that chemical reactions take place when particles of the reactants collide. They must collide with a certain minimum energy, called the activation energy. Chemical reactions involve the formation of bonds between atoms but often, before new bonds can be formed, old ones have to broken down. This means that there has to be enough energy (activation energy) to start breaking the old bonds before a reaction can occur. Most reactions are exothermic. I predict that this reaction between Hydrogen Peroxide, Amount of pH Buffer Solution and Potato is an exothermic reaction meaning that it is a reaction that gives out heat. The following diagram on the next page shows the breaking of old bonds and forming new bonds. [IMAGE] Break old bonds Form New Bonds [IMAGE][IMAGE] Energy Taken In Energy Given Out [IMAGE] An enzyme is a protein molecule that speeds up chemical reactions in all living things. Without enzymes, these reactions would occur too slowly or not at all, and no life would be possible.

All living cells make enzymes, but enzymes are not alive. Enzyme molecules function by changing other molecules. Enzymes are classified into several different categories, such as hydrolytic, oxidising, and reducing, depending on the type of reaction they manage. Hydrolytic enzymes accelerate reactions in which a substance is broken down into simpler compounds during reaction with water molecules. Oxidising enzymes, recognized as oxidises, accelerate oxidation reactions; reducing enzymes speed up reduction reactions, in which oxygen is removed. Enzymes combine with the transformed molecules to form a complex molecular structure in which chemical reactions occur. The enzyme, which remains unchanged, then breaks away from the product of the reaction. For that reason, an enzyme is a type of biological catalyst. Catalase is present in the peroxisomes (micro body organelles that house various oxidation reactions where toxic peroxides are made as side products) of nearly all-aerobic cells. It operates to protect the cell from the toxic effects of hydrogen peroxide by catalysing its disintegration into molecular oxygen and water lacking the production of free radicals (An atom or a group of atoms among an unpaired electron.

Radicals are unusually reactive and are capable of causing an extensive variety of biological damage). The active site is the location on the surface of the enzyme where the catalyzed reaction takes place. Enzyme reactions involve a substance (substrate) that is converted to another substance (product). [IMAGE] on the left shows how an enzyme works. The above given detail of what happens to the active site of the enzyme is what I predict will happen. 'For a reaction to occur, particles must collide. If the collision causes a chemical change it is referred to as a fruitful collision.' - (Hutchinson Encyclopaedia 2000). This led me to believe a greater concentration would mean there would be more collisions. The lower the concentration the less the gas particles collide meaning more time taken, the higher the concentration the more gas particles collide meaning less time taken for the predicted amount of hydrogen to collect in the measuring cylinder. The rate of reaction decreases with time, the concentration of the reactant decreases with time but the concentration of the product increases with time. I will be varying the pH of the Buffer Solution and I will be measuring the time.

I will keep some of the variables constant throughout the investigation such as the amount of potato and the amount of buffer solution. Also, the amount of Hydrogen Peroxide will be kept the same all the way through. Pre-Test In my pre-test, I will set up the apparatus as shown on the next page as the diagram. I will carry out my pre-test three times to make sure I get accurate results. The method I am going to use and the table that I will record my results in are below. Method: Ø Set up the apparatus as shown below in the diagram. Ø Mix up the buffer solutions according to which PH shall be tested first. Ø Measure out 4g of potato and place inside the conical flask. Ø Fill the trough with water and attach the delivery tube coming from the flask into the bottom of the measuring cylinder Ø Add 15ml of the buffer solution to the grated potato. Ø Measure 15ml of hydrogen peroxide into the syringe and quickly inject it into the buffer/potato mixture, and immediately replace the bung (ensuring is it air tight). Ø Start the stop clock immediately, and measure how much oxygen has collected in the graduated tube. Ø Repeat the experiment for each PH value.

Ø Record the results in a table like the one on the next page. Health & Safety: I will time these experiments for how long it takes for the volume of gas collected. Between each pre-test, I would say that there would be a ten-minute interval for me to record my results down in details and to set up for the next test. [IMAGE] Through completing my experiment I have found out that using a very concentrated Hydrogen Peroxide and pH Buffer Solution will definitely have an effect on the activity of Catalase. Patterns From Results Table After carrying out this experiment and obtaining my results, I have found out that the more concentrated the Hydrogen Peroxide and Buffer Solution is, the effect of pH on the activity of the Catalase will be stronger and quicker. Thus, the low concentrated Hydrogen Peroxide and Buffer Solution is, it took longer for 20cm³ of oxygen to collect in the measuring cylinder. This certain practical was based on what happened to the reaction when different amounts of pH Buffer Solutions were used; the higher Buffer Solutions had an increasing effect on the speed of the reaction. My graph looks good because the time is decreasing from high to low.

This is because ph 4.4 of the Buffer Solution was the least reactive when I carried out my experiment/practical. According to the graph, despite the fact that there are no anomalous results, if I had conducted the experiment a few more times then I would've obtained at least one or two unusual results. I conclude that the effect of pH on the activity of Catalase may be increased/quickened by using a stronger Buffer Solution; in this case pH 8.4. Increasing the concentration means keeping all of the other substances at a constant concentration. This means there are more particles of the Buffer Solution available in the reaction, and were altered to get a bunch of results. I am able to show this through the stronger and weaker Buffer Solutions on my table and graphs. 15ml of Buffer Solution at pH 8.4 produced the amount of oxygen required in 0.44cm³ per second. On the other hand, 15ml of Buffer Solution at pH 4.4 produced this amount of oxygen in 1.45cm³ per second.

We can clearly see that when the Buffer Solution's pH concentration is increased, this has the same effect on the speed of the reaction, which is the effect of pH on the activity of Catalase - it increases. With a change of pH the weak bonds holding the enzyme together will break. This will denature the enzyme, thus deactivating the active site. As enzymes normally exist within cells where the pH is 7, the most favourable pH is obviously 7. As you can see from the graph, a pH significantly higher or lower than 7 will kill the cells. Evaluating Experimental Work The experiment I carried out was suitable as the results and the graph were pleasing, seeing that my aim and prediction were proved correct, as what I predicted was accurate. I was lucky enough not to get unusual and unexpected results. This is because I measured everything correctly and carried out the experiment bearing in mind the fair test. Even if my results were good, they were not perfect, and I am able to explain four features that could improve my method. These could help develop my results further. A simple suggestion that could develop my method would be to handle equipment with measurements that go up in small steps.

For example, when we were measuring Hydrogen Peroxide or the pH Buffer Solution in the beaker, it would be difficult to be accurate. Despite the fact that this is not directly changing the method, one extra of less drop of Hydrogen Peroxide or pH Buffer Solution could practically influence our results. If there was air leaking from the measuring cylinder, that could stop our results corresponding to our prediction. In a case like this, it is not definite whether oxygen is leaking. To put a stop to this from happening, wedging the sides of the measuring cylinder with blue tack should make sure that no oxygen could escape. I think that the timing was accurate and reliable but only a second experiment would support that completely. I think that the equipment/apparatus I used was suitable for that particular experiment. I hardly had any problems with my experiment in finding out the effect of pH on the activity of catalase. Bibliography Ø Hutchinson Educational Encyclopaedia, 2000 Ø OCR Staged Assessment Phase 1 Module by Mary Janes Ø Energy and Chemistry Ø - searched for hydrogen peroxide, enzymes & catalysts.

The Effect of a Catalyst on Rate of Reaction - Chemistry LibreTexts The Effect of a Catalyst on Rate of Reaction Last updated Contributors This page explains how adding a catalyst affects the rate of a reaction. It assumes familiarity with basic concepts in the collision theory of reaction rates, and with the Maxwell-Boltzmann distribution of molecular energies in a gas. A catalyst is a substance which speeds up a reaction, but is chemically unchanged at its end. When the reaction has finished, the mass of catalyst is the same as at the beginning. Several examples of catalyzed reactions and their respective catalysts are given below: Manufacture of ammonia by the Haber Process iron Conversion of SO2 into SO3 during the Contact Process to make sulfuric acid vanadium(V) oxide, V2O5 Hydrogenation of a C=C double bond nickel The importance of activation energy Collisions only result in a reaction if the particles collide with a certain minimum energy called the activation energy for the reaction. The position of activation energy can be determined from a on a Maxwell-Boltzmann distribution: Only those particles represented by the area to the right of the activation energy will react when they collide. The majority do not have enough energy, and will simply bounce apart.

To increase the rate of a reaction, the number of successful collisions must be increased. One possible way of doing this is to provide an alternative way for the reaction to happen which has a lower activation energy. In other words, to move the activation energy to the left on the graph: Adding a catalyst has this effect on activation energy. A catalyst provides an alternative route for the reaction with a lower activation energy. This is illustrated on the following energy profile: A word of caution Care must be taken when discussing how a catalyst operates. A catalyst provides an alternative route for the reaction with a lower activation energy. It does not "lower the activation energy of the reaction". There is a subtle difference between the two statements that is easily illustrated with a simple analogy. Suppose there is a mountain between two valleys such that the only way for people to get from one valley to the other is over the mountain. Only the most active people will manage to get from one valley to the other. Now suppose a tunnel is cut through the mountain. Many more people will now manage to get from one valley to the other by this easier route. It could be said that the tunnel route has a lower activation energy than going over the mountain, but the mountain itself is not lowered.

The tunnel has provided an alternative route but has not lowered the original one. The original mountain is still there, and some people still choose to climb it. In chemical terms, if particles collide with enough energy they can still react in exactly the same way as if the catalyst was not there; it is simply that the majority of particles will react via the easier catalyzed route. Contributors There are no recommended articles. Article type The effect of catalysts on rates of reaction THE EFFECT OF CATALYSTS ON REACTION RATES This page describes and explains the way that adding a catalyst affects the rate of a reaction. It assumes that you are already familiar with basic ideas about the collision theory of reaction rates, and with the Maxwell-Boltzmann distribution of molecular energies in a gas. Note: If you haven't already read the page about collision theory , you should do so before you go on. Use the BACK button on your browser to return to this page, or come back via the rates of reaction menu. Note that this is only a preliminary look at catalysis as far as it affects rates of reaction. If you are looking for more detail, there is a separate section dealing with catalysts which you can access via a link at the bottom of the page.

The facts What are catalysts? A catalyst is a substance which speeds up a reaction, but is chemically unchanged at the end of the reaction. When the reaction has finished, you would have exactly the same mass of catalyst as you had at the beginning. Some examples Hydrogenation of a C=C double bond nickel Note: You can find details of these and other catalytic reactions by exploring the menu for the main section on catalysis. You will find a link at the bottom of this page. The explanation The key importance of activation energy Collisions only result in a reaction if the particles collide with a certain minimum energy called the activation energy for the reaction. Note: What follows assumes you have a reasonable idea about activation energy and its relationship with the Maxwell-Boltzmann distribution. This is covered on the introductory page about collision theory . If you aren't confident about this, follow this link, and use the BACK button on your browser to return to this page. You can mark the position of activation energy on a Maxwell-Boltzmann distribution to get a diagram like this: Only those particles represented by the area to the right of the activation energy will react when they collide. The great majority don't have enough energy, and will simply bounce apart.

Catalysts and activation energy To increase the rate of a reaction you need to increase the number of successful collisions. One possible way of doing this is to provide an alternative way for the reaction to happen which has a lower activation energy. In other words, to move the activation energy on the graph like this: Adding a catalyst has exactly this effect on activation energy. A catalyst provides an alternative route for the reaction. That alternative route has a lower activation energy. Showing this on an energy profile: A word of caution! Be very careful if you are asked about this in an exam. The correct form of words is "A catalyst provides an alternative route for the reaction with a lower activation energy." It does not "lower the activation energy of the reaction". There is a subtle difference between the two statements that is easily illustrated with a simple analogy. Suppose you have a mountain between two valleys so that the only way for people to get from one valley to the other is over the mountain. Only the most active people will manage to get from one valley to the other. Now suppose a tunnel is cut through the mountain. Many more people will now manage to get from one valley to the other by this easier route.

You could say that the tunnel route has a lower activation energy than going over the mountain. But you haven't lowered the mountain! The tunnel has provided an alternative route but hasn't lowered the original one. The original mountain is still there, and some people will still choose to climb it. In the chemistry case, if particles collide with enough energy they can still react in exactly the same way as if the catalyst wasn't there. It is simply that the majority of particles will react via the easier catalysed route. Questions to test your understanding If this is the first set of questions you have done, please read the introductory page before you start. You will need to use the BACK BUTTON on your browser to come back here afterwards. These questions cover all the various factors which affect rates of reaction, not just catalysts.

Question: What speeds up a chemical reaction, but is itself left unchanged?
Answer: A catalyst